Impingement Syndrome and Rotator Cuff Disease

The rotator cuff is a group of four tendons that fuse to form a flat sheet of tissue that surrounds the entire shoulder joint. These tendons connect to relatively small muscles which originate from the shoulder blade (scapula). When these muscles contract, they pull the tendons to rotate and elevate the arm relative to the body, and when they function in a coordinated fashion they compress the ball (humeral head) keeping it centered it in the socket (glenoid). As the shoulder moves, these tendons slide under two bony protrusions of the scapula, the acromion and the coracoid process, and the coracoacromial ligament which connects them. Between the uppermost tendon (supraspinatus) and the undersurface of the acromion is a lubricating sac (bursa). Impingement syndrome occurs when the supraspinatus tendon and bursa become inflamed and swollen from repeated pinching against the undersurface of the acromion during arm elevation, causing tendonitis and bursitis. This can occur as a result of repetitive overhead motion (especially in overhead athletes with increased laxity of the shoulder ligaments, abnormal positioning of the scapula, increased thickness or formation of a bone spur on the undersurface of the acromion, and/or thickening of the coracoacromial ligament. These patients frequently have pain in the front of the shoulder which is exacerbated by overhead reaching, throwing or lifting.

If the impingement persists over a prolonged period, fraying and tearing of the rotator cuff tendons (most commonly the supraspinatus) can occur. Some patients develop thinning and degeneration of the tendons as a result of the aging process. Less commonly, the rotator cuff may tear as a result of a trauma, such as a fall or an acute strain. When the rotator cuff tears, there is usually increased pain and weakness. In severe cases, there is loss of ability to raise the arm overhead or away from the body. There is frequently increased disturbance of sleep due to the pain. An orthopaedic surgeon can make the diagnosis by taking a complete history of the symptoms, examining the shoulder for weakness and tenderness, by reviewing special x-rays of the shoulder, and often by obtaining an MRI scan.

Shoulder Instability

Shoulder instability refers to disorders where the ball (humeral head) moves out of the socket (glenoid) either completely, as in a dislocation, or partially, as occurs in subluxation of the joint. In order for this to occur, there must be a disruption of either the ligaments that connect the ball and socket, the glenoid labrum which deepens the socket and allows for the attachment of the ligaments, or both. Although the humeral head can move in many directions, the most common situation occurs when the ball slides forward (anteriorly) out of the socket, which usually occurs when a backward force is placed on the arm when it is in the throwing position. When the shoulder dislocates, it must often be put back into place (reduced) in an emergency room. In cases where the instability is chronic, the patient has pain and a feeling of apprehension or looseness when the arm is placed in the throwing position, or when reaching overhead or out to the side.

Injuries to the Acromioclavicular Joint

The acromioclavicular joint (AC joint) is the connection between the end of the collar bone (clavicle) and the top the shoulder blade (acromion of the scapula). The joint is held together by a capsule and the clavicle is held in place by two strong ligaments (coracoclavicular ligaments). It is common for this joint to be large and prominent without causing symptoms. The acromioclavicular joint is most commonly injured by a fall or contact directly onto the point of the shoulder (AC joint sprain or shoulder separation) with resulting local pain and deformity. The ligaments and capsule can be stretched (Grade I), partially torn (Grade II), or completely torn (Grade III). The higher the degree of separation or dislocation, the greater the upward displacement of the clavicle relative to the acromion. In Grade III injuries the tip of the clavicle is a very prominent bump under the skin.

Degeneration of the acromioclavicular joint (arthropathy or arthritis) can occur over time with repetitive overhead use or shoulder trauma. There can be aching, stiffness clicking and/or swelling of the joint with significant pain when reaching overhead or across the body. Young people who lift heavy weights may develop the same symptoms as a result of erosion the end of the clavicle, a condition called distal clavicle osteolysis or weightlifter's shoulder.